Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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The length of the tanks is decided by determining the operating rates needed and knowing how long the immersion time must be for each process. The latter can sometimes be established by a series of laboratory-style experiments and required operating speeds calculated from total production requirements. Once these factors have been found, the length of the processing tank is calculated by the simple formula: Rate (ft/min.) immersion time (min.) = tank length (ft) A complete exercise to determine length might go, in part, like this: Required: 3 million of contact X per month 2 million of contact Y per month 1 million of contact Z per month Contacts/ft: X = 30; Y = 40; Z = 50 No. of feet req'd: X = 100,000; Y = 50,000; Z = 20,000 Total per month = 170,000 ft One shift operation, average 20 days per month 170,000/20 = 8,500 ft/day 8,500/7 hr = 1,215 ft/hr = 20.25 ft/min (25 to be safe) Immersion (dwell) time for Process A = 10 seconds B = 15 seconds Process A Tank: 25 ft/min. 0.167 min. = 4.175 ft Process B Tank: 25 ft/min. 0.25 min. = 6.25 ft The type of basis metal being plated, the condition of its surface, the size and design of the parts, and the type and amount of plating specified all have a direct effect on the time required to successfully pretreat and plate strip and pre- formed components. It is not possible to predict exactly how much time will be required for each step, but experience has shown that there are ranges of time that can be expected for most applications. Table I lists the approximate immersion or dwell times required for the vari- ous processes named. Experience has shown that most cleaners are usually able to do their job in 12 to 24 seconds on most materials. Electropolishing may require 5 to 15 seconds and acid activators 4 to 12 seconds. Plating times vary with the metals being plated, the deposition rates of each type of solution, and the current densities to be used. Current density, solution efficiency, deposition rate (at the current density used and in the type of plating cell employed), and the required thickness are the fac- tors used to calculate dwell times required for each type of plating solution. When proprietary solutions are purchased, the vendors usually can provide data for each of their plating solutions that enable fairly reliable estimates of the plating times required. When these data are not available, information in this Guidebook and other texts can be used to estimate how long a plating station will be required to obtain deposits of a specified thickness. As an example, the length of a tank required to obtain a nickel deposit of 0.000050 in. would be about seven feet if a production rate of 25 ft/min is planned and a current density of 200 A/ft2 is assumed (see Note that follows). Given: A-hr to deposit 0.0001 in. nickel = 1.9 (100% eff.) 1. 1.9/2 = 0.95 A-hr for 0.000050 in. 618

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